Forces in Truss Members (Statics)

[cpmustang07]

Homework Statement

See attachment.
Edit: Point A is a pinned connection (has a reactionary force in X and Y direction). Point B is a roller connection (only has reactionary force in Y direction)

Homework Equations

Sum Fx=0
Sum Fy=0
Sum of Moments=0

The Attempt at a Solution

Find reaction forces at point A and D. Normally this wouldn't be an issue. I'd just find the reaction force of D by solving for the moment around point A. Then find A by knowing that the sum of forces in Y direction is 0. However, dimensions are not given in the problem. I have the answers, but I do not see how to get to them.

After finding reaction forces, isolate each joint and begin with joint with no more than two unknowns. Proceed until all forces are found.

 

[PhanthomJay]

These are all equilateral triangles...each horizontal member has the same length, L. What would be the perp. distance from the applied load to A?

 

[cpmustang07]

These are all equilateral triangles...each horizontal member has the same length, L. What would be the perp. distance from the applied load to A?

3*cos(60)*L, correct?

 

[SammyS]

3*cos(60)*L, correct?

Interesting way to say 1.5L, which is correct.

 

[Phrak]

Interesting way to say 1.5L, which is correct.

No...

 

[PhanthomJay]

No...

Why not?? If the length of each horizontal member is L, the perpendicular distance from the line of action of the applied load to A is 1.5 L.

 

[Phrak]

Why not?? If the length of each horizontal member is L, the perpendicular distance from the line of action of the applied load to A is 1.5 L.

right. 1.5L to A and 1.5KN on D.

 

[cpmustang07]

Thank you for your help guys. I'll work on it again today and see if this different train of thought will get me through it. :)

I got it guys. Thank you. Apparently I'm really slow. ;)